In fuel cell stacks having a stack body in which a plurality of unit cells is stacked, in general, a load for fastening is applied by a fastening member in the stacking direction of the unit cells so as to fasten the stack body in order to reduce a contact resistance between unit cells and within each unit cell and to prevent leakage of a fluid (a fuel gas, an oxidant gas and cooling water) flowing within the fuel cell stack.
In such fuel cell stacks, if impact force is applied in a direction perpendicular to the stacking direction of the unit cells and the unit cells are misaligned in the direction perpendicular to the stacking direction due to the impact force, the unit cells may be misaligned to an extent that causes gas leakage. Specifically, examples of misalignments between unit cells that cause gas leakage may include a misalignment which causes a gasket to be twisted or broken or to fall out and a misalignment which causes a manifold of one unit cell to be moved to a position beyond a manifold sealing of an adjacent unit cell. Under such circumstances, various techniques have conventionally been proposed for suppressing misalignment in the direction perpendicular to the stacking direction of unit cells, i.e., for externally restricting a plurality of unit cells.
For example, Patent Document 1 below discloses a technique for providing an external restriction member for suppressing misalignment of a plurality of unit cells, which constitutes a stack body, in a direction perpendicular to the stacking direction. Specifically, a plurality of external restriction members is provided on the stack body in a state where the external restriction members are in contact, entirely across the stacking direction, with surfaces that are parallel to the stacking direction of the stack body.